There is a friction body in which changes color of thermochromic handwriting formed on a paper surface. The handwriting is changed its color by rubbing against the paper surface on which the handwriting is formed with any of those friction bodies. Then, the handwriting is visually recognized as being different that before the rubbing (see, e.g., Japanese Patent Unexamined Publication JP-A-2004-148744).
As the material of the friction body, there are exemplified an eraser, an elastomer and a plastic foam.
However, the eraser develops bits of grit during rubbing against paper surface and makes surroundings dirty, and besides, since the eraser is worn itself, it difficult to meet permanent use requirement.
On the other hand, the elastomer and the plastic foam don't have moderate friction coefficients due to their qualities and grades. When they have too large friction coefficients, rubbing them against paper surface sometimes leads to breakage of paper, wrinkling of paper or roughening (scuffing) of paper surface. Therefore, there occurs a problem that rewrite on rubbed areas becomes impossible or causes smearing to fail at forming good-quality handwriting. Contrary to the above case, too small friction coefficients of those friction bodies weaken the perception of rubbing. As a result, it is done unwittingly to rub paper with them under loads greater than necessary and the paper rubbed becomes uneven to spoil its appearance, and besides, the number of rubbings is apt to increase, and feelings of being inconvenient and tired are produced and such friction bodies come into disuse. Accordingly, their salability is impaired.